This application claims priority to Japanese Patent Application Number JP2001-333328 filed Oct. 30, 2001, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of producing an information recording medium, a production apparatus for the information recording medium, and an information recording medium produced by the production method.
2. Description of the Related Art
Recently, in the field of information recording, research on optical information recording systems is being conducted everywhere.
Optical information recording systems have numerous advantages such as the capability of non-contact recording and reproduction and the ability to handle various forms of memories such as read only types, write-once types, and rewritable types. Broad applications from industrial use to consumer use are being considered as systems enabling realization of inexpensive and large size files.
Increased capacity of optical recording media (hereinafter also referred to xe2x80x9coptical disksxe2x80x9d) for the above various types of optical information recording systems has been achieved mainly by shortening the wavelength of the laser light serving as the light source used in optical information recording systems and adopting objective lenses having high numerical apertures to reduce the spot size on a focal plane.
For example, in a CD (compact disk), the thickness of the disk substrate forming a light transmitting layer is about 1.2 mm, the wavelength of the laser light is 780 nm, the numerical aperture (NA) of the objective lens is 0.45, and the capacity is 650 MB, while in a DVD-ROM (digital versatile disk read-only memory), the thickness of the disk substrate forming a light transmitting layer is about 0.6 mm, the wavelength of the laser light is 650 nm, the NA is 0.6, and the capacity is 4.7 GB. A DVD is for example obtained by bonding together two disk substrate of about 0.6 mm thickness to form a disk having a thickness of 1.2 mm.
Furthermore, in the next generation optical disk systems, it is possible to increase the capacity to 22 GB or more by using an optical disk comprising an optical recording layer over which is formed a protection layer, that is, a light transmitting coating layer, reduced in thickness to about 0.1 mm, and making the laser light wavelength 450 nm or less and the NA 0.78 or greater.
FIG. 1A is a schematic perspective view of an optical disk for the above next generation optical disk system.
An optical disk DC forms an approximately disk shape with a center hole CH formed at a center portion thereof and is driven to rotate in a drive direction DR.
When recording or reproducing information, light LT such as a laser light of a blue to blue-violet color region is focused on the optical recording film in the optical disk DC by an objective lens OL having a numerical aperture of for example 0.8 or greater.
FIG. 1B is a schematic sectional view of the above optical disk.
Grooves for dividing track regions are provided in one surface of a disk substrate 30 having a thickness of about 1.1 mm formed of polycarbonate resin etc. An optical recording layer 31 comprised of for example a reflection film, a dielectric film, a recording film, another dielectric film, etc. stacked in that order is formed on this surface. The layer configuration and the number of layers of the optical recording layer 31 differ according to the type of recording material and the design.
The above recording film is for example a phase change type recording film, a magneto-optical recording film, or a recording film containing an organic dye.
Further, a light transmitting protection layer (coating layer) 32 having a film thickness of 0.1 mm comprised of for example an adhesive layer and a polymer film is formed on the optical recording layer 31.
When recording on or reproducing from the above optical disk, light LT such as laser light is focused by the objective lens OL to the optical recording layer 31 from the protection layer 32 side.
At the time of reproduction from the optical disk, returned light reflected at the optical recording layer 31 is received by a light-receiving element, a predetermined signal is generated by a signal processing circuit, and a reproduction signal is extracted.
A production method of the above optical disk shown in FIGS. 1A and 1B will be explained next.
First, for example, a disk substrate 30 comprised of for example polycarbonate resin is formed by injection molding using injection mold described below having a stamper for disk substrate which has a relief pattern for optical recording layer.
Next, an optical recording layer 31 is formed on the disk substrate.
Next, polycarbonate film is bonded to the optical recording layer 31 by adhesive layer to form the light transmitting protection layer (coating layer) 32 of 0.1 mm thickness.
The optical disk shown in FIGS. 1A and 1B can thus be formed.
FIG. 2 is a schematic view of the configuration of an injection molding mold for forming a disk substrate according to a conventional method.
An outer circumferential ring 61, a fixed side mirror 62, a fixed side temperature adjusting circuit 63, a stamper 64, and a sprue 65 are provided as fixed side mold parts at a fixed side attachment plate FT. On the other hand, a movable side mirror 67, a center pin 68, and a gate cut punch 69 are provided as movable side mold parts in movable side attachment plate MT. Resin is injected into a cavity 66 composed of the above parts to form a disk substrate.
However, in information recording medium including CDs, DVDs, and other optical disks, including next generation optical disks of the above configuration, and further hard disks, the disk substrates are generally formed by injection molding. In this case, however, a mold for the injection molding is configured by a plurality of parts. Clearance is inevitable between the parts. Therefore, burrs occur in the disk substrate formed.
Further, it is difficult to achieve a uniform surface precision of the parts or stamper. If step differences occur between the parts, the steps will also end up being transferred to the disk substrate formed.
Further, as shown in FIG. 3A, a bulge RD easily occurs at the outer circumferential ends of a disk substrate 30 formed by injection molding. In this case, the optical recording layer 31 is formed along the surface of the bulge RD.
If for example the protection layer film is bonded at the upper layer thereof by an adhesive layer to form the protection layer 32, as shown in FIG. 3B, an air bubble layer AL ends up occurring between the protection layer 32 and the optical recording layer 31, so use of the outer circumferential region RG becomes difficult.
Even when coating ultraviolet curing resin or other protection layer on the optical recording layer by spin coating, etc., the bulge of the outer circumferential end region is further accentuated and therefore it becomes impossible to use this region.
By adjusting the pressure for injecting the molten resin so as to suppress the occurrence of the bulge in the injection molding of the disk substrate, a recess where part of the substrate becomes thinner easily occurs and hence a new problem arises.
Disk substrates for optical disks were produced by the above injection molding and were examined for planarity.
Here, the disk substrates formed had the shape shown in FIGS. 4A to 4C, where FIG. 4A is a plan view of a signal surface, FIG. 4B is a side view thereof, and FIG. 4C is a plan view of a read surface.
In the figure, the positions of an innermost diameter (A), a sprue bushing (B), an air groove (C), a stamper holder (D), a signal portion (stamper) (E), an ejector (F), an ejector sleeve guide (G), a stacking rib (H), a mirror (I), and an outer circumferential end (Z) are shown.
FIG. 5A is a view showing the measurement results of the planarity in the vicinity of an outer circumferential end of a signal surface of the disk substrate according to the conventional method. The abscissa denotes a position on the disk X(mm), and the ordinate denotes a height of the surface Y(xcexcm).
This shows the occurrence of a bulge RD at the vicinity of the outer circumferential end Z.
FIG. 5B is a view showing the measurement results of the planarity in the vicinity of an outer circumferential end of a read surface of the disk substrate according to the conventional method. The abscissa denotes a position on the disk X(mm), while the ordinate denotes a height of the surface Y(xcexcm).
This shows the occurrence of a burr BR and bulge RD at the vicinity of the outer circumferential end Z.
FIG. 6A is a view showing the measurement results of the planarity in the vicinity of the outer circumferential end of a signal surface of a disk substrate formed by adjusting the pressure for injecting molten resin in the conventional method. The abscissa denotes a position on the disk X(mm), while the ordinate denotes a height of the surface Y(xcexcm).
The bulge RD in the vicinity of the outer circumferential end Z is suppressed, however, a recess RS where the disk becomes thinner occurs.
FIG. 6B is a view showing the measurement results of the planarity in the vicinity of an outer circumferential end of a read surface of a disk substrate formed while adjusting the pressure for injecting molten resin in the conventional method. The abscissa denotes a position on the disk X(mm), while the ordinate denotes a height of the surface Y(xcexcm).
The bulge RD in the vicinity of the outer circumferential end Z is suppressed, however, a recess RS where the disk becomes thinner occurs.
FIGS. 7A and 7B are views showing the measurement results of the planarity in the vicinity of the innermost diameter A of the signal surface of the disk substrate according to the conventional method divided into two sections. The abscissa denotes a position on the disk X(mm), while the ordinate denotes a height of the surface Y(xcexcm).
Occurrence of a burr (BR) and step difference (ST) was seen at an interface of the stamper holder (D) and the signal portion (stamper) (E). Further, a burr (BR) occurred at the innermost diameter A end or the like.
FIGS. 8A and 8B are views showing the measurement results of the planarity in the vicinity of the innermost diameter A of the read surface of the disk substrate according to the conventional method divided into two sections. The abscissa denotes a position on the disk X(mm), while the ordinate denotes a height of the surface Y(xcexcm).
At an interface of the ejector sleeve guide (G) and the mirror (I), occurrence of a slight burr (BR) and step difference (ST) was seen. Further, a step difference (ST) occurred at an interface of the ejector (F) and the ejector sleeve guide (G).
The method of forming a disk substrate by a compression molding is known. However, there is a problem that it needs long process time because resin is heated and made molten by mold and cooled after compression molding in the compression molding method.
Further, it is difficult to remove gas from resin in the time of compression molding, and vacuum exhaust is performed but it is not sufficient, therefore there is a problem that shape of the disk substrate becomes bad due to retaining air bubble in the resin.
Further, in a hard disk, bulge is formed when the injection molding is performed as well as the disk substrate of the optical disk, therefore the magnetic head floating with a clearance of several tens of nm ends up striking the surface of the hard disk due to this bulge.
An object of the present invention is to provide a method of a method of producing an information recording medium enabling production of disk substrate, etc. at a high productivity and enhanced planarity in an optical disk or other information recording medium, and to provide a production apparatus for producing the same and a information recording medium produced by such a method of producing.
To achieve the above object, the method of producing an information recording medium of the present invention comprises steps of: processing a surface of a disk substrate by satin-like finishing, heating and pressing the disk substrate through compression using a stamper having relief shapes so as to transfer the relief shapes to at least one satin-like finished surface of the disk substrate, forming a recording layer on the relief shape surface of the disk substrate, and forming a coating layer on the recording layer.
In the above method of producing an information recording medium, a surface of a disk substrate is processed by satin-like finishing in advance, then the disk substrate is heated and pressed through compression using a stamper having relief shapes so as to transfer the relief shapes to at least one satin-like finished surface of the disk substrate. Next, a recording layer is formed on the relief shape surface of the disk substrate, and a coating layer is formed on the recording layer.
Further, to achieve the above object, the method of producing an information recording medium of the present invention comprises steps of: processing a surface of a disk substrate by satin-like finishing, heating and pressing the disk substrate through compression using a stamper having relief shapes so as to transfer the relief shapes to at least one satin-like finished surface of the disk substrate, forming a first optical recording layer on the relief shape surface of the disk substrate, processing a surface of a resin sheet by satin-like finishing, heating and pressing the resin sheet through compression using a stamper having relief shapes so as to transfer the relief shapes to at least one satin-like finished surface of the resin sheet, forming a second optical recording layer on the relief shape surface of the resin sheet, bonding the first optical recording layer and the second optical recording layer.
In the above method of producing an information recording medium, a surface of a disk substrate is processed by satin-like finishing in advance, then the disk substrate is heated and pressed through compression using a stamper having relief shapes so as to transfer the relief shapes to at least one satin-like finished surface of the disk substrate. Next, a first optical recording layer is formed on the relief shape surface of the disk substrate. On the other hand, a surface of a resin sheet is processed by satin-like finishing in advance, then the resin sheet is heated and pressed through compression using a stamper having relief shapes so as to transfer the relief shapes to at least one satin-like finished surface of the resin sheet. Next, a second optical recording layer is formed on the relief shape surface of the resin sheet. Next, the first optical recording layer and the second optical recording layer are bonded.
Further, to achieve the above object, the production apparatus for an information recording medium of the present invention is a production apparatus for forming a substrate having relief shapes on at least one surface thereof of an information recording medium comprising the substrate and a recording layer formed on the relief shape surface of the substrate, the production apparatus of an information recording medium comprising: a mold for a compression molding having on an inside surface of a cavity thereof a stamper having relief shapes corresponding to the relief shapes, a heating means for heating the mold, and a pressing means for pressing the mold, the mold being split into an upper, center, and lower parts and being attached to a press movable vertically by the pressing means, a means for correcting parallelism of the lower mold and the upper mold of the press at the time of pressing of the press and making a pressing force uniform between the lower mold and upper mold being provided.
In the above production apparatus of an information recording medium of the present invention, the mold for a compression molding having on an inside surface of a cavity thereof a stamper having relief shapes corresponding to the relief shapes, is split into an upper, center, and lower parts and is attached to a press movable vertically by the pressing means, and a means for correcting parallelism of the lower mold and the upper mold of the press at the time of pressing of the press and making a pressing force uniform between the lower mold and upper mold is provided.
Further, to achieve the above object, the information recording medium of the present invention comprises a disk substrate having relief shapes on at least one surface thereof, a recording layer formed on the relief shape surface of the disk substrate, and a coating layer formed on the recording layer, the disk substrate being a disk substrate processed by a satin-like finishing of the surface thereof, then transferred with the relief shapes to the satin-like finished surface thereof by heating and pressing through compression molding using a stamper having relief shapes.
In the above information recording medium of the present invention, a recording layer and a coating layer are formed on the relief shape surface of the disk substrate which is processed by a satin-like finishing of the surface thereof, then transferred with the relief shapes to the satin-like finished surface thereof by heating and pressing through compression molding using a stamper having relief shapes.
Further, to achieve the above object, the information recording medium of the present invention comprises a disk substrate having relief shapes on at least one surface thereof, a first optical recording layer formed on the relief shape surface of the disk substrate, a resin sheet having relief shapes on at least one surface thereof, a second optical recording layer formed on the relief shape surface of the disk substrate, the first optical recording layer and the second optical recording layer being bonded, and light being focused from the resin sheet side for the disk substrate to the first optical recording layer and the second optical recording layer to record or reproduce information, wherein the disk substrate being a disk substrate processed by a satin-like finishing of the surface thereof, then transferred with the relief shapes to the satin-like finished surface thereof by heating and pressing through compression molding using a stamper having relief shapes, the resin sheet being a resin sheet processed by a satin-like finishing of the surface thereof, then transferred with the relief shapes to the satin-like finished surface thereof by heating and pressing through compression molding using a stamper having relief shapes.
In the above information recording medium of the present invention, a first optical recording layer is formed on the relief shape surface of the disk substrate which is processed by a satin-like finishing of the surface thereof, then transferred with the relief shapes to the satin-like finished surface thereof by heating and pressing through compression molding using a stamper having relief shapes, on the other hand, a second optical recording layer is formed on the relief shape surface of the resin sheet which is processed by a satin-like finishing of the surface thereof, then transferred with the relief shapes to the satin-like finished surface thereof by heating and pressing through compression molding using a stamper having relief shapes, and the first optical recording layer and the second optical recording layer is bonded.